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[email protected]://nina.ecse.rpi.edu/shur/

GaN Microwave Transistors

Michael S. Shur

Rensselaer Polytechnic Institute

Presented at NJIT on 11/09/05


Research Topics• Wide band gap electronics/photonics

– Deep UV LEDs– SAW acousto optoelectronics– Solid State Lighting– GaN Microwave Transistors

• THz plasma wave electronics• Modeling and simulation

– Unified Charge Control Model– Monte Carlo– 2D Circuit CAD (AIM-Spice)– HEMTs– TFTs– CMOS– HBTs

• Remote Internet Lab

600 500 400 300 200 100

0.00

0.03

0.06

0.09

0.12

0.15

Abs

orba

nce

Wavenumber (cm-1)

TNT

TNT

Si THz 300 K

0.5 1.0 1.5 2.00.00.20.40.60.81.0

0.0 0.3 0.6 0.9 1.0.00.10.20.30.40.50.60.70.80.91.0

120 GHz 3 THz

Phot

ores

pons

e (a

rb. u

nits

)

Vg (V)

x 60

Lg=30 nm

Vg(V)

Pho

tore

spon

se(a

.u.)

6 THz30 nm


GaN-based Microwave and MM Wave Field Effect Transistors

Rensselaer Polytechnic InstituteTroy, NY 12180, USA

Michael S. Shur

1970 1975 1980 1985 1990 1995 20000

100

200

300

400500

600700

800900

10001100

1200 INSPEC search query:Gallium Nitride

or Indium Nitrideor Aluminum Nitride

Num

ber o

f Pub

licat

ions

Year


Motivation: silicon is becoming a commodity

$0

$1,000

$2,000

$3,000

$4,000

$5,000

$6,000

Annual salary Value added Profit

ChinaIndiaBangladesh

Data for 2001 textile industry from Time, December 13 (2004). Page A16


Outline

• New physics of GaN-based FETs• Problems and solutions

– Gate lag and current collapse– 2D modeling– Field plates– MEMOCVD– MOSHFETs, MISHFETs, MISDHFETs

• High power and microwave switches• GaN FETs at THz frequencies• Conclusions


Nitride Advantages

•High mobility•High saturation velocity•High sheet carrier concentration•High breakdown field•Decent thermal conductivity•Growth on SiC substrate

•Chemical inertness•Good ohmic contacts•No micropipes

High power

Heat handling capability

Reliability should be possible

Properties Advantages

•SiO2/AlGaN and SiO2/GaN good quality interfaces Insulated

Gate


Figure of Meritfor high frequency/high power

CFOM =χε oµvsEB

2

χε oµvs EB2( )silicon

χ is thermal conductivityEB is breakdown fieldµ is low field mobilityvs is saturation velocity

εo is dielectric constant

0

200

400

Si GaAs 6H-SiC

4H-SiC GaN

Com

bine

d Fi

gure

of M

erit


Nitride DisadvantagesBlue emitters:NONE

UV emitters – low efficiency

Electronics:Reproducibility, ReliabilityYieldHence $130 M DARPA program


GaN Device History• 1932 – Roosevelt wins Presidential Election.

First GaN crystal synthesized (W. C. Johnson et al)• 1961 – Yuri Gagarin becomes the first man in space. First

p-type GaN (A. G. Fischer) • 1969 – First Moon walk by Armstrong and Aldrin. First

monograph on nonmetallic nitrides (G. V. Samsonov)• 1971- Bangladesh Independence. First GaN LED(J. I. Pankove and Paul Maruska)

• 1987- Dow Jones plunges 508 points (22.6%) on October 19 p-type activation via e-beam irradiation (Obyden S.K et al) RPI FRESHMEN conceived

(from Paul Maruska, A Brief History Of GaN Blue Light-Emitting Diodes, http://www.onr.navy.mil/sci_tech/information/312_electronics/ncsr/materials/gan/maruskastory.asp)


Potential and Existing Applications of Nitride Devices

• Blue, green, white light, and UV emitters– Traffic lights– Displays– Water, food, air sterilization and detection of biological

agents– Solid state lighting

• Visible-blind and solar-blind photodetectors• High power microwave sources• High power and microwave switches• Wireless communications• High temperature electronics• SAW and acousto-optoelectronics• Pyroelectric sensors• Terahertz electronics• Non volatile memories• Bioelectronics

Applications of U of V/RPI/SET quadrichromatic

Versatile Solid-State Lamp: Phototherapy of seasonal affective disorder at Psychiatric

Clinic of Vilnius University


Nitrides: New Symmetry, Hence New Physics

Zinc Blende Structure (GaAs)Diamond Structure (Si, Ge) Wurtzite Structure (SiC, GaN)

GaAs bouleSi boule AlN boule (Courtesy Crystal IS)


Nitride Heterostructures: Polarization Induced Electron and Hole 2D Gases

From A. Bykhovski, B. Gelmont, and M. S. Shur, J. Appl. Phys.74, p. 6734-6739 (1993)

AlGaN on GaN

From O. Ambacher et alJAP 87, 334 (2000)

46vC mcP 36


Strain from the lattice mismatch

• uxx = (aGaN -aAlGaN)/aGaN

• Ppe = 2 uxx (e31-e33 C13/C33)

How Piezoelectric constants are determined?

•Electromechanical coefficients (difficult)•Optical experiments (indirect)•Estimate from transport measurements (very indirect)


Spontaneous polarization

For comparison, in BaTiO3, Ps = 0.25 C/m2 (1.93x1015cm-2)Carrier density in AlGaAs/GaAs is ~ 1012 cm-2

-0.0453.47 1014

-0.0574.39 1014

-0.0322.46 1014

-0.0292.23 1014

-0.0816.24 1014

Spontaneous polarization(C/m2)(cm-2)

BeOZnOInNGaNAlNAfter F. Bernardini et al. Phys Rev. 56, 10024(1997)


Both Spontaneous and Piezo Polarizations are Important

GaN

GaN

GaN

AlGaN

AlGaN

AlGaN

Relaxed

Relaxed

TensileStrain

CompressiveStrain

Relaxed

Relaxed

GaN

GaN

GaN

AlGaN

AlGaN

AlGaN

Psp

Psp

Psp

Psp

Ppe

Ppe

Psp

Psp

Ppe

Ppe

Psp

Psp

PspPsp

+σ

+σ

-σ +σ

-σ

-σ

[0001] [0001]

Ga face N face

After O. Ambacher et al. J.Appl. Phys. 85, 3222 (1999)

2D electrons

2D holes

2D holes

2D electrons


Polarization Doping in AlGaN/GaN Heterostructures

A l M o la r F r a c t io n

0

1

2

3

4

5

6

0 0 .2 0 .4 0 .6 0 .8 1

From M. S. Shur, A. D. Bykhovski, R. Gaska, and A. Khan, GaN-based Pyroelectronicsand Piezoelectronics, in Handbook of Thin Film Devices, Volume 1: Hetero-structures for High Performance Devices, Edited by Colin E.C. Wood, pp. 299-339,

Academic Press, San Diego, 2000

• •

•

•

•0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100 120Thickness, nm

abrupt interface

graded interface

R. Gaska, A. D. Bykhovski, M. S. Shur, Piezoelectric Doping and Elastic Strain Relaxation in AlGaN/GaN HFETs, pp. 435-458, Appl. Phys. Lett. Vol. 73, No. 24, 3577 (1998)


Effect of Strain on Dislocation-Free Growth

• Critical thickness as a function of Al mole fraction in AlxGa1-xN/GaN: superlattice (solid line), SIS structure (dashed line).

From A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, J. Appl. Phys. 81 (9), 6332-6338 (1997)

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1

Al Mole Fraction

Thickness, nm

100 200 300 400 500 600

1,000

2,000

3,000

300K

77K

Hal

l Mob

ility

(cm

2 /Vs)

AlGaN Thickness (A)

Effect of Critical Thickness on Electron Mobility


New physics of electron/hole transport

•Large polar optical phonon energy (x 3 GaAs) - Quasi-elastic polar optical scattering

•Ultra dense 2D gas (x 20)

•Electron “runaway” dominant

•Strange holes/ strange acceptors

After V.T. Masselink, Applied Physics Letters, vol. 67(6), 801-805, 1995

EEC2 EC3

Vdr

VC3

VC2 3D

2D

EEC2 EC3

Vdr

VC3

VC2 3D

2D


New physics of electron transport

•Large polar optical phonon energy (x 3 GaAs) - Quasi-elastic polar optical scattering•Ultra dense 2D gas (x 20)•Electron “runaway” dominant

After V.T. Masselink, Applied Physics Letters, vol. 67(6), 801-805, 1995

EEC2 EC3

Vdr

VC3

VC2 3D

2D

EEC2 EC3

Vdr

VC3

VC2 3D

2D

From A. Dmitriev, V. Kachorovskii, M. S. Shur, and M. Stroscio, Electron Drift Velocity of Two Dimensional Electron Gas in Compound SemiconductorsInternational Journal of High Speed Electronics and Systems, Invited, Volume 10, No 1, pp. 103-110, March 2000

21

2

1 am∝δ

22

2

2 am∝δ

m1 << m2 ⇒δ1 >> δ 2

2

1


Consequence of high polar optical energy: two step optical polar scattering process

Active region

Passive region

From B. Gelmont, K. S. Kim, and M. S. Shur, J. Appl. Phys. 74, 1818 (1993)

ω0

K = 0.6

K = 0K = 0.3

mob

ility

(cm

2 /V

s )

0

100

1,000

1017 1018 1019

Doping (cm-3)


Comparison of Runaway in 2D and 3D Systems

3D Case•Deformation scattering on acoustic and optical phonons does not lead to runaway•Polar optical scattering (forward!) leads to runaway

2D Case•Even deformation scattering leads to runaway


High Drift Velocity and high mobility

.

0

1

2

3

0 100 200 300Electric Field (kV/cm)

2

GaN

Vel

ocity

(100

,000

m/s

)

GaAs

SiC

Si

> 2,000 cm2/V-s (300 K)see R. Gaska, J. W. Yang, A. Osinsky, Q. Chen,M. Asif Khan, A. O. Orlov, G. L. Snider, M. S. Shur, Appl. Phys. Lett., 72, 707, 1998

3

2

1

0

300 K500 K1,000 K

0.1 0.2 0.3

Electric field (MV/cm)

GaN 3

2

1

0 5 10 15 20

300 K500 K1,000 K

GaAs

Electric field (kV/cm)

(a) (b)

Fig. 1 a is from U. V. Bhapkar, and M. S. Shur, Monte Carlo Simulation of Electron Transport in Wurtzite GaN, J. Appl. Phys., 82 (4), pp. 1649-1655,August 15 (1997)

0

2

4

6

8

10

0 0.1 0.2 0.3

Distance [micron]

Velo

city

[107 c

m/s

]

75 kV/cm

600 kV/cm

200 kV/cm

150 kV/cm

After B. E. Foutz, S. K. O'Leary, M. S. Shur,and L. F. Eastman. Appl. Phys., vol. 85, . 7727 (1999)


Velocity-Field Curves for Nitride Family

InN is the fastest nitride material

From B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman, J. Appl. Phys. 85, 7727 (1999)


Electron mobility (over 2,000 cm2/V-s)

0 1 2 3 4

600

900

1,200

1,500

1,800

2,100

2D Electron Density (x 101 3 cm-2)

Hal

l Mob

ility

(cm

2 /V-s

)Al0 .2Ga0.8N-GaN


Overshoot in GaN

Below 150 kV/cm little or no overshoot occursAt 200 kV/cm modest overshoot occurs over 0.3 micronAt 600 kV/cm high velocity occurs below 0.1 micron

0

2

4

6

8

10

0 0.1 0.2 0.3

Distance [micron]

Velo

city

[107 c

m/s

]

75 kV/cm

600 kV/cm

200 kV/cm

150 kV/cm

After B. E. Foutz, S. K. O'Leary, M. S. Shur, and L. F. Eastman, Transient Electron Transport in Gallium Nitride, Indium Nitride, and Aluminum NitrideJ. Appl. Phys., vol. 85, No. 11, pp. 7727-7734 (1999)


Higher Breakdown Field in Heterostructures?

Breakdown field might be determined by cladding layers(see M. Dyakonov and M. S. Shur, Consequences of Space

Dependence of Effective Mass in Heterostructures, J. Appl. Phys. Vol. 84, No. 7, pp. 3726-3730, October 1 (1998)

AlGaN

AlGaNGaN Quantum WellWavefunction

Large current carrying capabilities are combine with large voltage blocking capabilities


Thermal Conductivity versus Temperature

Si data after Glassbrenner and Slack (1964)

GaN data after Sichel and Pankove (1977)

Thick red line - theoretical expectations for pureGaN based on Pankove data and anharmonicity mechanism

10 100 1000

1

10

100

0.1Ther

mal

Co n

duc t

ivity

( W c

m-1

K-1

)

Temperature (K)

GaN

Si


Nitride-based FETs – promises and problems

Promises• 30 W/mm at 10 GHz versus 1.5 W/mm for GaAs• 150 W – 240 W per chip• Highest cutoff frequency so far 152 GHz Problems• Gate leakage• Gate lag and current collapse• Reliability• YieldSolutions• Strain energy band engineering• MEMOCVDtm

• Insulated gate designs• Gate edge engineering

M. A. Khan, M. S. Shur, Q. C. Chen, and J. N. Kuznia, Current-Voltage Characteristic Collapse in AlGaN/GaN Heterostructure Insulated Gate Field Effect Transistors at High Drain Bias, Electronics Letters, Vol. 30, No. 25, p. 2175-2176, Dec. 8, 1994


High Electron Sheet Density Allows for a New Approach: AlGaN/GaN MISFET

M. A. Khan, M. S. Shur, Q. C. Chen, and J. N. Kuznia, Current-Voltage Characteristic Collapse in AlGaN/GaN Heterostructure Insulated Gate Field Effect Transistors at High Drain Bias, Electronics Letters, Vol. 30, No. 25, p. 2175-2176, Dec. 8, 1994


MOSHFET (SiO2 )

I-SiC

Pd/Ag/AuGaN AlN

Pd/Ag/AuAlInGaN

S G D

SiO2

AlGaN/ InGaN GaN DHFET

I-SiC

Pd/Ag/AuGaN AlN

InGaN AlInGaN

S G D

Si3N4 /SiO2

I-SiC

Pd/Ag/AuGaN AlN

InGaN AlInGaN

S G D

MISDHFET

MISHFET Si3N4 I-SiC

Pd/Ag/AuGaN AlN

Pd/Ag/AuAlInGaN

S G D

Si3N4Reducing the gate leakage current (104 - 106 times)

Reducing current collapse, Improving carrier confinement

Combining the advantages

Resolving the issues: AlGaInN, gate dielectrics, InGaN channel


Unified charge control model (UCCM) and Real Space Transfer

V V a n n V nnGT F s th

s− = − +⎛⎝⎜

⎞⎠⎟α η( ) ln0

0MOSFETs and HFETs

www.aimspice.com

From S. Saygi, A. Koudymov, S. Rai, V. Adivarahan, J. Yang, G. Simin, M. Asif Khan, J. Deng, M.S. Shur, and R. Gaska, Real Space Electron Transfer in III-Nitride Metal-Oxide-Semiconductor-Heterojunction (MOSH) Structures, Appl. Phys. Lett., accepted for publication


Real Space Transfer in MOSHFETs

From S. Saygi, A. Koudymov, S. Rai, V. Adivarahan, J. Yang, G. Simin, M. Asif Khan, J. Deng, M.S. Shur, and R. Gaska, Real Space Electron Transfer in III-Nitride Metal-Oxide-Semiconductor-Heterojunction (MOSH) Structures, Appl. Phys. Lett., accepted for publication


MOSHFET Gate Leakage

1. E- 08

1. E- 07

1. E- 06

1. E- 05

1. E- 04

1. E- 03

1. E- 02

1. E- 01

- 10 - 5 0 5Voltage ( V )

Gat

e Cu

rrent

Den

sity

(A/c

m^2

)

25oC

50oC

75oC100oC

150oC

Traps and leakage:Complexities of highly non-ideal systems

From F. W. Clarke, Fat Duen Ho, M. A. Khan, G. Simin, J. Yang, R. Gaska, M. S. Shur, J. Deng, S. Karmalkar, Gate Current Modeling for Insulating Gate III-N Heterostructure Field-Effect Transistors, Mat. Res. Symp. Proc. Vol. 743, L 9.10 (2003)


Trapping in Nitrides:Reverse Gate Leakage Modeling

Direct tunneling and trap-assisted tunnelingFrom S. Karmalkar, D. Mahaveer Sathaiya, M. S. Shur, Mechanism of the Reverse Gate Leakage in AlGaN / GaNHEMTs, Appl. Phys. Lett. 82, 3976-3978 (2003)


Comparison with Experiment

From S. Karmalkar, D. Mahaveer Sathaiya, M. S. Shur, Mechanism of the Reverse Gate Leakage in AlGaN / GaNHEMTs, Appl. Phys. Lett. 82, 3976-3978 (2003)


Doped channel GaN/AlGaN HFETs for Higher Power

. 2

-20 20 40

0

Ener

gy (e

V)

Distance (nm)

Undoped

Nd = 5x1017 cm-3 1

After M. S. Shur, GaN and related materials for high power applications, Mat. Res. Soc. Proc. Vol. 483, pp. 15-26 (1998)


MOSHFET Switch

0 100 200 300 400 500 6000

5

10

15

20

- 6 V

- 3 V

0 V

+ 3 V

Vg = + 6 V

PON/OFF = 7.5 kW/mm2

R ON = 75 mOhm-mm2

Cur

rent

, A/m

m2

Drain Voltage, V

15 µm source-drain spacingAfter G. Simin, X. Hu, N. Ilinskaya, A. Kumar, A. Koudymov, J. Zhang, M. Asif Khan, R. Gaska and M. S. ShurA 7.5 kW/mm2 current switch using AlGaN/GaN Metal-Oxide-Semiconductor Heterostructure Field Effect Transistors on SiC Substrates, Electronics Letters. Vol. 36 Issue: 24, pp. 2043 –2044, Nov. 2000

• 75 mOhm×mm2

• 2 - 3 times less than that reported for buried channel SiC FETs

• 25-100 times less than that for SiC induced channel MOSFETs


MOSHFET Technology for Power Electronics

Switching speeds1,000 times higher than for Si IGBTs can be achieved (up to GHz range

Commensurate decrease in power supply weight, cost and reliability due to dramatic decrease in size and weight of reactive components

Big improvement in power qualityEnergy markets: “future energy”

102 103 10410-8

10-6

10-4

10-2

100

102

Breakdown Voltage (V)

GaN

Si

SiC

re

GBONsp

EVR

εµ

5.72310725.8 −−×=

R ON

sp (Ω

2 )

From J.L Hudgins, G.S. SiminE. Santi, and M.A. Khan, IEEE Transactions on Power Electronics, vol. 18, no. 3, May 2003


Applications

10 100 10, 0001,0 0010 -2

10 0

10 2

10 3

10 1

10 -1D is p layd ri ve s

T e le c o m m u -ni c a tio ns

F a c to ryA u to m at io n

Mo to rCo n t ro l

L a m pB a l la s t

T ra c t io nHD V C

B lo c k in g vo l ta g e ( V )

PowerSupplies

Automotive

GaNregion

Cur

ren t

(A)

GaN-UF

SiC-ABBGaN-UF

SiC-Purdue

GaN-UF

SiC-NCSU

SiC-RPI

GaN-Caltech

6H-SiC

4H-SiC

GaN

AlGaN-UF

AlGaN

B r e a k d o w n V o l ta g e (V )

Sp

eci

fic

Re

sist

an

ce (

oh

m-c

m2

)

101 102 103 10410-4

10-3

10-2

10-1

100

MG-MOSHFET

Data from B. J. Baliga, IEEE Trans., ED-43, p. 1717 (1996)


Design Example

MOSHFET Switch, x10 voltage x3 currentDramatic improvement in yield and reliability

After G. Simin and M. Asif Khan, M. S. Shur, R. Gaska, High-power switching using III-Nitride Metal-Oxide Semiconductor Heterostructures, International Journal of High Speed Electronics and Systems, Vol. XX, No. X 1-14 (2005)

+

+

-

-

-

-

+

+

L G1

G2 G3

G4


Field Plate

From S. Karmalkar, M. S. Shur, and R. Gaska, GaN-based power high electron mobility transistors, in 'Wide Energy Bandgap Electronic Devices”, pp. 173-216, Fan Ren and John Zolper, Editors, World Scientific (2003), ISBN 981-238-246-1

n-AlGaN 1 x 1016 / cm3 0.02 µm

n-GaN 1 x 1015 / cm3 0.03 µm

0.5 µm 1 µm Vg Ldg

Silicon nitride, 0.3 µm

Vd

2-DEG, 1x1013 / cm2 p-GaN, 1.5 x 1016 / cm3

2 µm 2 µm

1 x 1018 / cm3 0.05 µm tp


No Field Plate, One Field PlateTwo Field Plates

0 2 4 6 8 100

1

2

3 Drain FPGate FP

B

C

A

Elec

tric

Fiel

d (M

V / c

m)

Distance from Source (µm)

0 200 400 600 800 1000 12000

1

2

3

Dra

in C

urre

nt (

mA/

mm

)

Drain Bias ( V )

0

10

20

30B

C

A



RESURF Effect

0 2 4 6 8 10 120

200

400

600

800

1000

1200

Grounded substrate

Field plates andp-n junction

Ideal

Floatingsubstrate

Field plates only

Bre

akdo

wn

volta

ge, V

br (V

)

Drain to gate separation, Ldg (µm)



GaN 1/f Noise Surprises

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+0110

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

GaN[8]

Si [1-2]

GaAs[1-2]

SiC [3-4]

GaN HFETon Sapphire [8-9]

GaAsHEMTs [5]

GaN HFETon SiC [9]

Si NMOS [6-7]

GaN MOS-HFET [10]

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+0110

10-7

10-6

10-5

10-4

10-3

10-2

10-1

110

10-7

10-6

10-5

10-4

10-3

10-2

10-1

1

GaN[8]

Si [1-2]

GaAs[1-2]

SiC [3-4]

GaN HFETon Sapphire [8-9]

GaAsHEMTs [5]

GaN HFETon SiC [9]

Si NMOS [6-7]

GaN MOS-HFET [10]

Device noise is smaller than materials noise!!!


Where the traps are (from GR noise)

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.24 eV [42]

AlGaN thin films

1 eV [54]

1.6 eV [41]

0.2 eV [38]1-3 meV [30]

0.35-0.36 eV [36,38]

0.42 eV [37]

0.85 eV [38]

1 eV [4]1 eV [33]

EC

AlGaN/InGaN/GaN heterostructures

AlGaN/GaN heterostructures

GaNphotodetectors

Ene

rgy

E (

eV)

From S. L. Rumyantsev, Nezih Pala, M. E. Levinshtein, M. S. Shur, R. Gaska, M. Asif Khan and G. Simin, Generation-Recombination Noise in GaN-based Devices, from GaN-based Materials and Devices: Growth, Fabrication, Characterization and Performance, M. S. Shur and R. Davis,

Editors, World Scientific, 2004


0

10

20

30

40

50

60

-10 -8 -6 -4 -2

Idc(VG= 0)

VG(t)

Id (return @ VG= 0)

VG= 0

Id (VG)

Current collapse

Tarakji, G. Simin, N. Ilinskaya, X. Hu, A. Kumar, A. Koudymov, J. Zhang,and M. Asif Khan, M.S. Shur and R. Gaska, Appl. Phys. Lett., 78, N 15, pp.

2169-2171 (2001) G. Simin, A. Koudymov, A. Tarakji , X. Hu, J. Yang and

M. Asif Khan, M. S. Shur and R. Gaska APL October 15 2001

VG

Gate Lag and Current collapse in AlGaN/GaN HFETs:Pulsed measurements of “return current”

Time

Time

IDS

VT

“Return” current

Current collapse


Nearly Identical Gate Lag Current Collapse was observed in:

I-SiC/Sapphire

Pd/Ag/AuGaN AlN

AlGaN S G D

I-SiC/Sapphire

Pd/Ag/AuGaN AlN

n-GaN S G D

GaN MESFET AlGaN/GaN HFET AlGaN/GaN MOSHFET

I-SiC

Pd/Ag/AuGaN AlN

AlGaN

S G D

SiO2

0 20 40 60 80 100 120 1400.00.20.40.60.81.01.21.41.61.82.02.22.4

R, k

Ω

LG, µm

R(0) R(τ)

LG

• AlGaN cap layer is not primarily responsible for CC

• Only the gate edge regions contribute to the CC

GTLM pattern (LG variable, LGS= LGD =const)


Electron temperature contour map VD = 10V and VS = VG = 0V

From N. Braga, R. Gaska, R. Mickevicius, M. S. Shur, M. Asif Khan, G. Simin, Simulation of Hot Electron and Quantum Effects in AlGaN/GaN HFET, submitted to JAP

Importance of gate edge engineeringconfirmed


Mechanism of current collapse in GaN FETs

• Current collapse is not related to AlGaN layer alone

• Current collapse is caused by trapping at gate edges

• Current collapse can be eliminated by using DHFET structures

• Current collapse time delay correlates with 1/f noise spectrum

• SOLVE THE CURRENT COLLAPSE ISSUE BY CHANNEL AND GATE EDGE ENGINEERING


G. Simin et.al. Jpn. J. Appl. Phys. Vol.40 No.11A pp.L1142 - L1144 (2001)

• Better 2DEG confinement and Partial strain compensation• Significantly reduced carrier spillover

•No current collapse

I-SiC

Pd/Ag/Au

GaN

AlN

InGaN (x ≤ 5%, 50 A) AlGaN (x=0.25,250 A)

S G D

I-SiC

Pd/Ag/Au

GaN

AlN

InGaN (x ≤ 5%, 50 A) AlGaN (x=0.25,250 A)

S G DS G D S G D

1017

1016

1014

~0.1 µm

Regular HFET InGaN channel DHFET

1014

~0.05 µm

InGaN channel DHFET Design – 2D simulationsG-Pisces (VG= -1; VD = 20 V)


From R. Gaska, M. Asif Khan, and M. S. Shur, III-nitride based UV light emitting diodes, pp. 59-76 in UV Solid-State Light Emitters and Detectors. Proc. NATO ARW, Series II, Vol. 144, ed. By M. S. Shur and A. Zukauskas, Kluwer, Dordrecht, 2004

Strain and Energy Band Engineering

•Graded composition profile and quaternary AlGaInN •Superlattice buffers for strain relief•PALE and MEMOCVD epitaxial growth•Homoepitaxial substrates•Non-polar substrates

0.0 0.2 0.4 0.6 0.8 1.00

10

20

30

40

50

60

70

Thic

knes

s (n

m)

Al molar fractionFrom A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, Elastic Strain Relaxation in GaN-AlN Superlattices, Proceedings of International Semiconductor Device Research Symposium, Vol. II, pp. 541-544, Charlottesville, VA, ISBN 1-880920-04-4, Dec. 1995


Effect of Strain on Dislocation-Free Growth

• Critical thickness as a function of Al mole fraction in AlxGa1-xN/GaN: superlattice (solid line), SIS structure (dashed line).

From A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, J. Appl. Phys. 81 (9), 6332-6338 (1997)

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1

Al Mole Fraction

Thickness, nm

100 200 300 400 500 600

1,000

2,000

3,000

300K

77K

Hal

l Mob

ility

(cm

2 /Vs)

AlGaN Thickness (A)

Effect of Critical Thickness on Electron Mobility


MOs

NH3

Surface roughening

Pre-reaction!!!

gas-phase reaction and low surface migration

Growth front

Growth steps

Conventional MOCVDConventional MOCVD


MOs

NH3

Minimized pre-reaction

Enhanced migration

allowing V/III separation hence reducinggas-phase reaction & enhancing surface migration

Growth front

Growth steps

MEMOCVDMEMOCVDTMTM


AlInGaN HFETs on 4AlInGaN HFETs on 4”” SubstratesSubstrates

AlAl0.250.25GaGa0.750.75N/GaNN/GaN44”” sapphiresapphire

8 mm edge exclusion8 mm edge exclusion

3.2 3.4 3.6 3.8 4.0 4.2 4.4

0

2000

4000

6000 5

4

321

PL

Inte

nsity

(a.u

.)

Photon Enenrgy (eV)

Room temperature PL mapping of 4” diameter AlGaN/GaN HFET wafer

22 22 23 23 24

Al%22 22 23 23 2422 22 23 23 24

Al%

AlAl-- variation < 2% over 4variation < 2% over 4”” waferwafer

MEMOCVDMEMOCVD™™


Bulk AlN (400 µm)

Pd/Ag/Au

GaN (0.3 µm)Epitaxial AlN (0.3 µm)

Pd/Ag/Au

AlGaN (22 nm)

SourceGate

Drain

AlGaN/ GaN HFET

Makes surface smoother

Al molar fraction 29%Substrate from Crystal IS

HEMT structure design on Bulk AlN substrate


-2 0 2 4 6 8 10 12 14 16 180.00.10.20.30.40.50.60.70.80.91.0

Max. VGS=+5V;1V step

Dra

in C

urre

nt, A

/mm

VDS, V

Devices on AlN comparable to those on semi-insulating SiCDevices with W = 1 mm (multi finger) have been fabricated

Lg ~ 1.5 mm, Lgs ~ 1 mm, Ldg ~ 4 mm

Large positive Vgs > 5 V applied

Much larger than for HEMTs on SiC

DC characteristics of AlGaN/GaN HEMT device


-10 -5 0 5 10 15 20 25-202468

10121416182022242628

PAE

Gain

POut

Dev. Eff. Width = 100 µm

2.2 W/mm

4.1 W/mm

VDS=25 V VDS=45 V

PO

ut, d

Bm

; G

ain,

dB

; P

AE

, %

Delivered Input Power, dBm

RF characteristics of AlGaN/GaN HEMT device

4 GHz


Inverted channel design to be explored

AlN

InGaN

DrainSourceGate 1

n-type AlGaInN

AlN

InGaN

DrainSourceGate 1

n-type modulation doped AlGaInN

SET, patent pending


Plasma Wave THz DevicesDeep submicron FETs can operate in a new PLASMA regime at frequencies up to 20 times higher than for conventional transit mode of operation

-600 -500 -400 -300 -200 -100 0

0

1

2

3

4

5

C

B

A

Res

onan

t Pea

k (a

.u.)

Gate Voltage(mV)

THz emission from 60 nm InGaAs HEMTResonant detectionOf sub-THz and THz

0 2 4 6 8 10 1202468

101214161820

0 1 2 30.0

0.5

1.0

0.2 0.4 0.6 0.8

0.4

0.6

0.8

1.0

InGaAs-HEMT

f (TH

z)

Usd (V)f (THz)

Em

issi

on (a

.u.)

Emis

sion

Inte

nsity

(a.U

.)

Detection Frequency (THz)

InSb-bulka)

b)

From W. Knap, J. Lusakowski, T. Parenty, S. Bollaert, A. Cappy, V. Popov, and M. S. Shur, Emission of terahertz radiation by plasma waves in sub-0.1 micron AlInAs/InGaAs high electron mobility transistors, Appl. Phys. Lett. , March 29 (2004)


GaN Microwave Detector

0 5 10 15 20

0

5

10

15

20(a)GaN HFET

f ( GHz )

R

( V/W

)

Measured DataCalculated (x0.25)

0.0 0.5 1.0 1.5 2.0

0

100

200

300(b)

From J. Lu, M. S. Shur, R. Weikle, and M. I. Dyakonov, Detection of Microwave Radiation by Electronic Fluid in AlGaN/GaN High Electron Mobility Transistors, in Proceedings of Sixteenth Biennial Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits, Ithaca, New York, Aug. 4-6 (1997), pp. 211-217


GaN-based Plasma Wave Electronics

-4 -2 0 2 4

0.0

2.0

4.0

6.0

8.0 T=8 K, GaN HEMT600 GHz

Indu

ced

V s-Vd (m

V) (L

ock-

In X

Out

put)

Vg (V)50 75 100 125 150 175 200 225 250

0.0

1.0

2.0

3.0

4.0

5.0

Inte

nsity

(a.u

.)

Frequency (GHz)

Radiation intensity from 1.5 micron GaN HFET at 8 K.

600 GHz radiation response of GaN HEMT at 8 K

8 GHz cutoff


Electronic island at the surface of semiconductor grain in pyroelectric matrix

(MQDs -Moveable Quantum Dots)

Control by external field – zero dimensional Field Effect (ZFE)

Po

Semiconductor

Electronic island

PyroelectricPo

Semiconductor

Electronic inversion island

Pyroelectric

Hole inversion island

Inversion electron and hole islands at the surface of pyroelectric grain in semiconductor matrix

After V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)


Terahertz oscillations

MOVABLE QUANTUM DOTS (MQD)

CAN SWITCH OR SHIFT FREQUENCY BY EXTERNAL FIELD OR BY LIGHT

1 THz to 30 THz

2D island might oscillate as a whole over grain surface. The oscillations can be exited by AC field perpendicular to Po

00

4( 2 )p

ePmR

=+

πωε ε

Oscillation frequency is of the order of a terahertz

0 2~ω π/

Oscillation frequency

After V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)


New Physics of Movable Quantum Dots• Self-assembled quantum dot arrays• Coulomb blockade• Light concentration in quantum dots• Left handed materials

• Terahertz detectors• Terahertz emitters• Terahertz mixers• Photonic terahertz devices• Photonic crystals• Plasmonic crystals• Solar cells and thermo voltaic cells

New Potential Applications


Sponsors

NATO

HumboldtFoundation


I owe a debt of gratitude to my students, postdocs, and collaborators around the Globe


New device physics of nitride based materialsEnables new applicationsRequires new designs and new modeling approaches

GaN based microwave devicesFactor of 10 to 30 advantage in powerInsulated gate has an advantage

THz plasma wave electronics devicesGaN has an advantageBoth resonant detectors and emitters are possible

Conclusions

Documents

GaN Microwave Transistors - Information Services and ...ieeenj/archived_slides/2005-11-09_EDSCASMTT.pdf · – GaN Microwave Transistors ... – Unified Charge Control Model – Monte